Caller protected stack return address in a hardware managed stack architecture

ABSTRACT

Corruption of program stacks is detected by using guard words placed in the program stacks. A called routine executing on a processor checks a guard word in a stack of a calling routine. The checking determines whether the guard word has an expected value. Based on determining the guard word has an unexpected value, an indication of corruption of the stack is provided. Some routines, however, may not support use of guard words. Thus, routines that are interlinked may have differing protection capabilities. A determination is made as to the differing protection capabilities, an indication of the same is provided, and the routines are executed without failing due to the differing protection capabilities.

PRIOR APPLICATION

This application is a continuation of co-pending U.S. application Ser. No. 14/989,397, entitled “CALLER PROTECTED STACK RETURN ADDRESS IN A HARDWARE MANAGED STACK ARCHITECTURE,” filed Jan. 6, 2016, which is hereby incorporated herein by reference in its entirety.

BACKGROUND

One or more aspects relate, in general, to processing within a computing environment, and in particular, to protecting data of the computing environment.

Corruption of computer programs may occur in many forms. One such form is the overwriting of data causing the program to perform tasks or return to addresses that are unexpected. This corruption may be innocent or malicious. As a particular example, the corruption may occur in a call stack (also referred to as a stack) used by a computer program to store information about the active subroutines of the computer program. For example, a stack is used to keep track of the point to which an active subroutine should return control (i.e., return address) when the routine finishes executing. An active subroutine is one that has been called, but is yet to complete execution. Such activations of subroutines may be nested to any level (recursive as a special case), hence the stack structure. Stacks may be corrupted by overwriting the return addresses, thereby having a called subroutine return to an unexpected location.

Again, the overwriting of the return address may be innocent or malicious, but regardless, is to be detected and planned for such that the program or other data is not corrupted.

SUMMARY

Shortcomings of the prior art are overcome and additional advantages are provided through the provision of a computer program product for detecting corruption of stacks of a computing environment. The computer program product includes a computer readable storage medium readable by a processing circuit and storing instructions for performing a method. The method includes checking, by a called routine executing on a processor of the computing environment, a guard word provided by a calling routine, the calling routine having called the called routine, and the guard word being stored in a stack of the calling routine and protecting a return address stored directly into the stack by a hardware instruction; determining, based on the checking, whether the guard word has an expected value; and based on determining the guard word has an unexpected value, providing an indication of corruption of the stack.

Computer-implemented methods and systems relating to one or more aspects are also described and claimed herein. Further, services relating to one or more aspects are also described and may be claimed herein.

Additional features and advantages are realized through the techniques described herein. Other embodiments and aspects are described in detail herein and are considered a part of the claimed aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more aspects are particularly pointed out and distinctly claimed as examples in the claims at the conclusion of the specification. The foregoing and objects, features, and advantages of one or more aspects are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 depicts one example of a computer system/server of a computing environment to incorporate and/or use one or more aspects of the present invention;

FIG. 2A depicts another example of a computing environment to incorporate and/or use one or more aspects of the present invention;

FIG. 2B depicts further details of the memory of FIG. 2A;

FIG. 3A depicts one example of a stack used in accordance with an aspect of the present invention;

FIG. 3B depicts one example of a buffer overflow;

FIGS. 4A-4E depict examples of stack frames and a guard word used in accordance with an aspect of the present invention;

FIGS. 5A-5B depict one embodiment of logic to detect corruption of stacks, in accordance with an aspect of the present invention;

FIG. 6 depicts one example of a Store Guard Word instruction, in accordance with an aspect of the present invention;

FIG. 7 depicts one example of a guard word register, in accordance with an aspect of the present invention;

FIG. 8 depicts one example of a POPCHECK instruction, in accordance with an aspect of the present invention;

FIG. 9 depicts one example of logic of a static linker, in accordance with an aspect of the present invention;

FIG. 10 depicts one example of logic of a dynamic linker, in accordance with an aspect of the present invention;

FIG. 11 depicts one example of logic of a Store Guard Word Conditional instruction, in accordance with an aspect of the present invention;

FIG. 12 depicts one example of logic of a POPCHECK Conditional instruction, in accordance with an aspect of the present invention;

FIG. 13 depicts one example of an enable vector of indicators used in accordance with an aspect of the present invention;

FIG. 14 depicts another example of logic of a Store Guard Word Conditional instruction, in accordance with an aspect of the present invention;

FIG. 15 depicts another example of logic of a POPCHECK Conditional instruction, in accordance with an aspect of the present invention;

FIGS. 16A & 16B depict one example of logic relating to detecting corruption of stacks, in accordance with an aspect of the present invention;

FIG. 17 depicts one embodiment of a cloud computing environment; and

FIG. 18 depicts one example of abstraction model layers.

DETAILED DESCRIPTION

One or more aspects relate to using a guard word to protect a call stack. The guard word is included in the call stack and checked by one or more called routines. If the checking indicates the guard word is different than expected (i.e., has been changed), then an indication of a corrupt stack is provided.

In one example, architected guard word instructions (e.g., hardware instructions) are provided to initialize and verify a stack guard word in order to prevent code injection/execution attacks from malicious system users. Use of the guard word instructions may facilitate using the guard word and/or enhance system security.

In yet a further aspect, it is recognized that not all routines or modules (e.g., one or more routines) that may be linked with one another, e.g., by being called from a routine or otherwise, may support the guard word protection facility, and therefore, one or more features are provided that enable such routines or modules with differing protection capabilities to be interlinked without causing a fatal error.

One embodiment of a computing environment to incorporate and/or use one or more aspects of the present invention is described with reference to FIG. 1. In one example, computing environment 100 includes at least one computer system/server 102, which is operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well-known computing systems, environments, and/or configurations that may be suitable for use with computer system/server 102 include, but are not limited to, personal computer systems, server computer systems, thin clients, thick clients, handheld or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputer systems, mainframe computer systems, and distributed cloud computing environments that include any of the above systems or devices, and the like.

Computer system/server 102 may be described in the general context of computer system-executable instructions, such as program modules, being executed by a computer system. Generally, program modules may include routines, programs, objects, components, logic, data structures, and so on that perform particular tasks or implement particular abstract data types.

As depicted in FIG. 1, computer system/server 102 is shown in the form of a general-purpose computing device. The components of computer system/server 102 may include, but are not limited to, one or more processors or processing units 106, a system memory 108, and a bus 110 that couples various system components including system memory 108 to processor 106.

In one embodiment, processor 106 is based on the z/Architecture offered by International Business Machines Corporation, or other architectures offered by International Business Machines Corporation. z/Architecture is a registered trademark of International Business Machines Corporation, Armonk, N.Y., USA. Other names used herein may be registered trademarks, trademarks, or product names of International Business Machines Corporation or other companies. One embodiment of the z/Architecture is described in “z/Architecture Principles of Operation,” IBM Publication No. SA22-7832-10, March 2015, which is hereby incorporated herein by reference in its entirety.

In other examples, processor 106 may be based on other architectures, such as an x86 architecture offered by Intel Corporation, Santa Clara, Calif., and/or other architectures offered by Intel or other companies. In one example, the architecture in which processor 106 is based is a Complex Instruction Set Computing (CISC) architecture. The examples provided herein are not meant to be limiting in any manner.

Processor 106 includes, in one embodiment, stack corruption detection logic 160 used to determine whether a guard word in a stack has an unexpected value, therefore, indicating that a return address in the stack has been overwritten. Stack corruption detection logic 160 may use, in one embodiment, instructions to initialize and verify the guard word, and/or the interlinking features described herein.

Bus 110 represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus.

Computer system/server 102 typically includes a variety of computer system readable media. Such media may be any available media that is accessible by computer system/server 102, and it includes both volatile and non-volatile media, removable and non-removable media.

System memory 108 can include computer system readable media in the form of volatile memory, such as random access memory (RAM) 112 and/or cache memory 114. Computer system/server 102 may further include other removable/non-removable, volatile/non-volatile computer system storage media. By way of example only, storage system 116 can be provided for reading from and writing to a non-removable, non-volatile magnetic media (not shown and typically called a “hard drive”). Although not shown, a magnetic disk drive for reading from and writing to a removable, non-volatile magnetic disk (e.g., a “floppy disk”), and an optical disk drive for reading from or writing to a removable, non-volatile optical disk such as a CD-ROM, DVD-ROM or other optical media can be provided. In such instances, each can be connected to bus 110 by one or more data media interfaces. As will be further depicted and described below, memory 108 may include at least one program product having a set (e.g., at least one) of program modules that are configured to carry out the functions of embodiments of the invention.

Program/utility 120, having a set (at least one) of program modules 122, may be stored in memory 108 by way of example, and not limitation, as well as an operating system, one or more application programs, other program modules, and program data. Each of the operating system, one or more application programs, other program modules, and program data or some combination thereof, may include an implementation of a networking environment. Program modules 122 generally carry out the functions and/or methodologies of embodiments of the invention as described herein.

Computer system/server 102 may also communicate with one or more external devices 130 such as a keyboard, a pointing device, a display 132, etc.; one or more devices that enable a user to interact with computer system/server 102; and/or any devices (e.g., network card, modem, etc.) that enable computer system/server 102 to communicate with one or more other computing devices. Such communication can occur via Input/Output (I/O) interfaces 140. Still yet, computer system/server 102 can communicate with one or more networks such as a local area network (LAN), a general wide area network (WAN), and/or a public network (e.g., the Internet) via network adapter 150. As depicted, network adapter 150 communicates with the other components of computer system/server 102 via bus 110. It should be understood that although not shown, other hardware and/or software components could be used in conjunction with computer system/server 102. Examples, include, but are not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data archival storage systems, etc.

Another embodiment of a computing environment to incorporate and use one or more aspects is described with reference to FIG. 2A. In this example, a computing environment 200 includes, for instance, a native central processing unit 202, a memory 204, and one or more input/output devices and/or interfaces 206 coupled to one another via, for example, one or more buses 208 and/or other connections. As examples, computing environment 200 may include a zSeries server offered by International Business Machines Corporation, Armonk, N.Y.; an x86 processor offered by Intel Corporation, Santa Clara, Calif.; an HP Superdome with Intel Itanium II processors offered by Hewlett Packard Co., Palo Alto, Calif.; and/or other machines based on architectures offered by International Business Machines Corporation, Hewlett Packard, Intel, Oracle, or others.

Native central processing unit 202 includes one or more native registers 210, such as one or more general purpose registers and/or one or more special purpose registers used during processing within the environment. These registers include information that represents the state of the environment at any particular point in time.

Moreover, native central processing unit 202 executes instructions and code that are stored in memory 204. In one particular example, the central processing unit executes emulator code 212 stored in memory 204. This code enables the processing environment configured in one architecture to emulate another architecture. For instance, emulator code 212 allows machines based on architectures other than the z/Architecture, such as x86 servers, HP Superdome servers or others, to emulate the z/Architecture and to execute software and instructions developed based on the z/Architecture. Other architectures may also be emulated.

Further details relating to emulator code 212 are described with reference to FIG. 2B. Guest instructions 250 stored in memory 204 comprise software instructions (e.g., correlating to machine instructions) that were developed to be executed in an architecture other than that of native CPU 202. For example, guest instructions 250 may have been designed to execute on a z/Architecture processor, but instead, are being emulated on native CPU 202, which may be, for example, an Intel Itanium II processor. In one example, emulator code 212 includes an instruction fetching routine 252 to obtain one or more guest instructions 250 from memory 204, and to optionally provide local buffering for the instructions obtained. It also includes an instruction translation routine 254 to determine the type of guest instruction that has been obtained and to translate the guest instruction into one or more corresponding native instructions 256. This translation includes, for instance, identifying the function to be performed by the guest instruction and choosing the native instruction(s) to perform that function.

Further, emulator code 212 includes an emulation control routine 260 to cause the native instructions to be executed. Emulation control routine 260 may cause native CPU 202 to execute a routine of native instructions that emulate one or more previously obtained guest instructions and, at the conclusion of such execution, return control to the instruction fetch routine to emulate the obtaining of the next guest instruction or a group of guest instructions. Execution of the native instructions 256 may include loading data into a register from memory 204; storing data back to memory from a register; or performing some type of arithmetic or logic operation, as determined by the translation routine.

Each routine is, for instance, implemented in software, which is stored in memory and executed by native central processing unit 202. In other examples, one or more of the routines or operations are implemented in firmware, hardware, software or some combination thereof. The registers of the emulated processor may be emulated using registers 210 of the native CPU or by using locations in memory 204. In embodiments, guest instructions 250, native instructions 256 and emulator code 212 may reside in the same memory or may be disbursed among different memory devices.

As used herein, firmware includes, e.g., the microcode, millicode and/or macrocode of the processor. It includes, for instance, the hardware-level instructions and/or data structures used in implementation of higher level machine code. In one embodiment, it includes, for instance, proprietary code that is typically delivered as microcode that includes trusted software or microcode specific to the underlying hardware and controls operating system access to the system hardware.

Within a processing environment, a stack is used by a routine to track the point at which the routine should return control when it finishes executing. As used herein, a routine is program code, and may include a subroutine, function, method, etc. One routine may be called by another routine. The one routine performing the calling is referred to as the calling routine or the caller routine, and the routine being called is referred to as the called routine or the callee routine. One example of a stack is described with reference to FIG. 3A. This stack may be in memory 108, as an example.

As shown in FIG. 3A, a stack 300 includes a plurality of stack frames, such as stack frames 302 a, 302 b. A stack frame is a frame of data that gets pushed onto the stack. The data of a stack frame may vary; however, in one example, a stack frame 302 a includes a stack pointer 304; a parameter area 306 passed to a called routine; a local and spill variable area 308 of a calling routine; a buffer 310; and a register save area 312 of one or more registers for use by a called routine and to be restored prior to returning. Further, a return address 314 is placed between the current stack frame and a previous stack frame 302 b. A stack frame may include additional, less and/or different data than described herein.

One form of corruption related to computer processing is to overflow buffer 310, in which more data than can be accepted by the buffer is written to the buffer, overflowing the buffer and overwriting return address 314, as depicted in FIG. 3B at 350. In overwriting the return address, a different address may be placed there directing the returning routine to other code that may perform a task that should not be performed and may even be malicious.

Thus, in accordance with an aspect of the present invention, a guard word is provided to detect such overflow. The guard word may be any value (e.g., numerical, alphanumeric, alphabetic, include symbols, etc.), and may be any desired size. The position of the guard word is agreed upon by the routines, in one example, or at least an indication of the position is provided to the routines that use the stack frame. In one embodiment, the presence and location of a guard word is specified by an application binary interface (ABI).

One example of adding a guard word to a stack is described with reference to FIGS. 4A-4E. First, referring to FIG. 4A, an initial state of a caller's stack frame 400 of a call stack is shown having a stack pointer 402. Thereafter, as shown in FIG. 4B, a guard word 404 is inserted ahead of the caller's stack frame. That is, the guard word is stored in a location in memory that is in the direction of stack growth, such as when a callee routine is called by the caller, the callee creates its stack frame, but skips this location. Thus, the guard word is placed between the caller's stack frame and the callee's stack frame. The creation of the callee's stack frame creates a stack having the caller's stack frame and the callee's stack frame. Further, since the guard word is between the two frames, the guard word written by the caller is now part of the call stack.

In one example, the caller stores a guard word at (ESP-size of (return address)-size of (guard word), where ESP is extended stack pointer) prior to performing the first subroutine call. (In another embodiment, for a stack that grows upward, the address to store the guard word is computed as (SP)+size of (return address), where SP is stack pointer). In another embodiment, the placement further takes into account a number of function parameters which may be placed on the stack prior to a function (or other routine) call. Thus, in one embodiment, the guard word may be placed at an address ESP-size of (return address)-size of (guard word)-size of parameter area), for a stack growing downward, i.e., from higher to lower addresses.

Further, as depicted in FIG. 4C, based on a subroutine call (e.g., function call) in accordance with a microprocessor implementing a hardware managed function call stack, a return address 406 is pushed onto the stack in accordance with a hardware definition. In accordance with one embodiment, this results in the return address being inserted onto the stack between the guard word and the caller's stack frame, and the stack pointer is moved. As indicated, in one example, the return address is inserted onto the stack via a hardware push return stack. For instance, in a CISC architecture, a jump subroutine function deposits the return address directly onto the hardware implemented processor stack.

Additionally, referring to FIG. 4D, a called routine, which is called by the caller routine and referred to as the callee, allocates its stack frame 420. In allocating its stack frame, the callee is careful not to overwrite the guard word. In one embodiment, for a callee enabled in accordance with an aspect of the present invention, a programmer or compiler determining the size of a callee stack frame treats the word location corresponding to the guard word as reserved, and no data is allocated thereto in the stack frame. However, to ensure that the guard word is properly preserved, the stack pointer is updated by the callee to skip the guard word in a separate instruction, or the size of the stack frame to be allocated is increased by the size of the guard word in the allocation on the stack to prevent it from being overwritten.

In contrast, in a callee not enabled in accordance with aspects of the present invention and called by a caller enabled with a protective guard word mechanism, the callee stack frame is allocated so as to overwrite the guard word with a portion of the callee's stack frame's data.

In one embodiment, after the callee completes processing, the callee checks the guard word and if it has an expected value, then the callee returns to the return address, and in so doing, removes the return address, as depicted in FIG. 4E at 430.

In accordance with one or more aspects, the guard word is provided by the caller routine and verified by the called routine, as described below. The caller writes the guard word once, e.g., when it first allocates a stack frame; and that once written guard word is used by one or more callees. That is, the guard word protects returns from the one or more callees. Each callee checks the guard word prior to returning to determine whether it has an expected value. If it does have the expected value, then the callee returns to the return address, as expected. Otherwise, an indication of a corrupt guard word is provided. Further, the program may be terminated and/or the operating system is notified to take additional actions against intrusion. In one aspect, this reduces the number of store instructions to be executed to write a guard word compared to embodiments where a store of a guard word corresponds to each function (or other routine) call, and a check of a guard word corresponds to each function (or other routine) return. Thus, the cost of the protection mechanism is reduced. Further, in another aspect, it is ensured that guard words are available from the cache rather than the store queue, because they were written much earlier than being checked. Consequently, an expensive forwarding operation from the store queue, often resulting in additional penalties may be avoided, and thereby further improving performance.

Further details relating to using a guard word for stack protection are described with reference to FIGS. 5A-5B. With reference to FIG. 5A, one embodiment of actions taken by a caller are described, and with reference to FIG. 5B, one embodiment of actions taken by a callee are described.

Referring to FIG. 5A, in one embodiment, a caller routine stores a guard word, e.g., ahead of the caller's stack frame, STEP 500. The caller routine then places function call parameters on the caller's stack frame, STEP 502. In one example, the parameter size for all calls is matched in order to re-use the guard word (i.e., a parameter area of constant size is assigned and allocated to all routines called by the present routine leaving some parameter space unused by routine calls corresponding to a smaller parameter area based on the number and type of parameters specified in such call. Then, the caller calls a callee routine, and a return address is pushed onto the stack by the hardware, in this example, STEP 504. Processing associated with the callee routine is described with reference to FIG. 5B.

Referring to FIG. 5B, based on being called, the callee allocates is stack frame, making sure to skip the guard word, STEP 550. The callee then optionally performs one or more functions, STEP 552. The callee then un-stacks the frame including the guard word, STEP 554. That is, the callee de-allocates the stack frame and moves the stack pointer over the guard word. The callee checks the guard word, STEP 556, and determines whether the guard word was as expected, INQUIRY 558. If the guard word was not the expected value, an indication of corruption is provided, STEP 560. Otherwise, the callee returns to the return address, STEP 562.

One example of code to write a guard word, verify a guard word, and prevent the return to a corrupted return address is provided below (in one embodiment based on a CISC instruction set architecture):

Subroutine call: Store Guard Word -20 [ESP] push [var]    ; Push last parameter first push 216    ; Push the second parameter push eax    ; Push first parameter last call_myFunc    ; Call the function add esp, 12    ; Remove the 3 parms upon return Callee     .486     .Model Flat     .Code     PUBLIC_myFunc     _myFunc Proc     ;Subrouting Prolog     SUB ESP, 4    ; Skip Guard Word push ebp    ; Save the old base pointer move ebp, esp    ; Set the new base pointer value sub esp, 4    ; Make room for one 4-byte local variable push edi    ; Save the values of registers function     push esi    ; Will modify. This func uses EDI and ESI ; Subroutine Body     <attack occurs here>     ; Subroutine Epilog     pop esi    ; Recover register values pop edi     move sp, ebp    ; Deallocate local variables pop ebp    ; Restore the caller's base pointer value POPCHECK    ; Pop and check guard word Ret    ; Obtain and remove address of caller from    stack; return to caller

In the above code, a Store Guard Word instruction is used to provide a memory location in which the guard word is to be saved; and a POPCHECK instruction is used to verify the guard word's correctness, each of which is described below.

As shown in FIG. 6, a Store Guard Word instruction 600 has the following format, in one embodiment: STORE GUARD WORD address. In operation, a guard word value is read from a specified location, such as a special purpose register, a control register, a secure memory location, etc., and stored in a temporary location (rtmp). Then, the value stored in the temporary location is stored at the address 602 provided by the instruction (e.g., ST rtmp, address).

In one example, the specified location may be a guard word register. For instance, as depicted in FIG. 7, a guard word register 700 includes a guard word value 702 that is read and stored in the stack.

Further, as shown in FIG. 8, an instruction, referred to as POPCHECK, 800 obtains, in one example, the top of stack (TOS) word from a stack (e.g., a caller's stack), treats the obtained word as a guard word, moves the stack pointer such that the word remains unmodified in storage but is no longer considered to be on the stack, and tests whether the retrieved word is a correct guard word or whether corruption has occurred. In the case of corruption, an indication of corruption is provided. This may include, for instance, a transfer to a fixed address, transferring to an event based branch, raising an exception; and/or transferring to supervisor software, etc.

One example of pseudo code for the POPCHECK instruction is, as follows:

LD rtmp1, [ESP]      # load word from top of stack ADD ESP, ESP, 4      # move stack pointer Rtmp <= read from guard word location If (rtmp not equal to rtmp1)  Indicate corruption

In a further embodiment, POPCHECK may be combined with a return to provide a POPCHECKRET instruction. One example of pseudo code for the POPCHECKRET instruction, as follows:

LDD ra, 4[ESP]     # load double word (for 64b mode) LD rtmp1, [ESP]     # load word from top of stack ADD ESP, ESP, 12     # move stack pointer, skipping guard word     and return address Rtmp <= read from guard word location If (rtmp not equal to rtmp1)  Indicate corruption Branch to ra

In one aspect, the POPCHECKRET instruction may access the return address from memory prior to accessing the guard word to be checked, to eliminate any period during which the return address may be unprotected by a protective guard word. In one embodiment, POPCHECKRET is implemented as a single instruction in the architecture, such as the x86 instruction set architecture. In another embodiment, a sequence of two instructions (e.g., POPCHECK and RET) or more instructions (e.g., an example sequence including: LOAD GUARD WORD; COMPARE loaded guard word to reference guard word; BRANCH to notification address; RET, or another sequence) is recognized by the instruction decode logic, and transformed into a single internal instruction, e.g., using known instruction decode time optimization. Such an embodiment may be executed on a processor not implementing a single POPCHECKRET sequence in hardware but with lesser security, and on processors that implement a POPCHECKRET operation on which higher security may be achieved, thus combining both program portability to processors not enabled with one or more hardware function aspects of the present invention, and higher security on processors that implement such aspects.

As described above, a guard word is placed in a stack and is used by one or more callees to detect whether a return address has been overwritten. This detects corruption of the stack and prevents further corruption of data and/or programs. Additionally, the transfer of control to an undesired or unknown location is prevented.

In accordance with one or more further aspects, modules (e.g., a module includes one or more routines) or routines that may be linked to one another, e.g., by being called by a routine or otherwise, may have differing protection capabilities. For instance, a caller routine may support the guard word protection facility, but one or more of the routines called by the caller may not support the guard word protection facility, or vice versa. This may cause problems, e.g., when the caller program is expecting an action not performed by the callee routine or vice versa. Thus, in accordance with an aspect of the present invention, one or more features are provided that allow routines or modules of differing protection capabilities to be linked without failing.

As one example, one aspect includes using a protection guard enablement indicator to indicate whether the guard word facility is to be used. As one example, a protection guard enablement indicator is provided for each software thread (or process or application, or in a single threaded core, a core). The protection guard enablement indicator is provided in the context switch information accessed by an operating system; or hypervisor or other virtual machine manager in a computing environment including logical partitions and/or virtual machines.

Based on a module loader recognizing that at least one routine which is not protected is loaded (as indicated by a protection indicator for the routine or for a module containing the routine), the protection guard enablement indicator is set to disable guard protection use. In a further embodiment, a dynamic linker may recognize this situation, and disable the guard protection use, if it is to be disabled. Further details relating to the use of the protection guard enablement indicator are described with reference to FIGS. 9-10.

With reference to FIG. 9, processing associated with a static linker is described. This processing may be performed in conjunction with other processing performed by the static linker. In one example, the first module is, e.g., the main program. In another embodiment, each routine is a module, and the stack guard support is indicated on a per-routine basis.

Referring to FIG. 9, a static linker executing within a processor receives an instruction to link modules (a module includes one or more routines, in one embodiment), STEP 900. Based thereon, a variable referred to as stack_guard is set equal to true, STEP 902. A module, such as a first module, is accessed, STEP 904, and a determination is made as to whether this module supports stack guard protection (also referred to herein as conditional guards), INQUIRY 906. This is determined, for instance, based on a protection indicator associated with the module. This protection indicator may be stored in a memory location or a file location associated with the module, as examples.

If the protection indicator is set, e.g., to one, then the module supports stack guard protection. However, if it is not set, e.g. is equal to zero, then the module does not support stack guard protection. If the module does not support stack guard protection, then stack_guard is set to false, STEP 908.

Thereafter, or if the module does support stack guard protection, then a determination is made as to whether another module is to be linked, INQUIRY 910. If so, processing continues to STEP 904. Otherwise, a check is made of the value of stack_guard, INQUIRY 912. If stack_guard is set to true, then the linked modules are written to a linked module file as a linked module and indicating that the linked module supports stack guards, STEP 914. However, if stack_guard is set to false, then the linked modules are written to the linked module file as a linked module and indicating that the linked module does not support stack guards, STEP 916. This allows the modules to be processed even though they have differing protection capabilities. They either are executed in accordance with stack guard protection if the modules support such protection, or are executed without this protection, if one or more of the modules do not support stack guard protection.

With reference to FIG. 10, processing associated with a dynamic linker is described. This processing may be performed in conjunction with other processing performed by the dynamic linker. Modules processed by the dynamic linker may correspond to modules statically linked, as described above.

Referring to FIG. 10, an indicator referred to as a protection guard enablement indicator is set (e.g., to one) to specify stack guards are enabled, STEP 1000. A requested module is loaded, STEP 1002, and a determination is made as to whether the loaded module supports stack guard protection, INQUIRY 1004. For instance, the module's protection indicator is checked to determine if it is set to enabled. If the loaded module does not support stack guard protection, then the protection guard enablement indicator is reset (e.g., set to zero) to indicate that stack guards are to be disabled, STEP 1006. Thereafter, or if the module supports stack guard protection, the code in the loaded module is executed, STEP 1008. Again, either the module is executed with stack guard protection, based on the module supporting this protection, or is executed without stack guard protection, based on the module not supporting stack guard protection.

Further, a determination is made as to whether another module is to be loaded, INQUIRY 1010. If not, the program terminates, STEP 1012. Otherwise, processing continues with STEP 1002.

With the above logic, when at least one module of a plurality of modules to be linked does not support stack guard protection, then stack guard protection is not used. Thus, in one example, verification of the guard word may be suppressed, and in a further aspect, the storing of the guard word may also be suppressed.

To facilitate suppressing the storing of the guard word and/or verifying the guard word in selected situations, such as one or more of the routines or modules does not support stack guard protection, variants of the Store Guard Word and POPCHECK or POPCHECKRET instructions are provided that include conditional logic to check whether stack guard protection is to be used. These instructions are referred to as a Store Guard Word Conditional (STPGC) instruction and a POPCHECK Conditional (POPCHECKC) or POPCHECKRET Conditional instruction, respectively. Each of these instructions has a format similar to the Store Guard Word or POPCHECK/POPCHECKRET instruction, respectively, except the opcode would be different indicating whether or not the conditional logic is included.

In one embodiment, with the Store Guard Word Conditional instruction, the guard word is stored in the specified memory location in the call stack, if the protection guard enablement indicator is enabled; and for the POPCHECK/POPCHECKRET instruction, the verification is performed, if the protection guard enablement indicator is enabled. In one example, the check of the protection guard enablement indicator is implemented in the instruction decode unit of the processor. In such an embodiment, if the protection guard enablement indicator indicates that the protection guard facility is not to be used, the instruction decode logic may translate the instruction to a no-operation (NOP) instruction, or completely omit it from the stream of decoded instructions.

Further details relating to the Store Guard Word Conditional instruction are described with reference to FIG. 11. In one embodiment, based on initiating execution of the Store Guard Word Conditional instruction, STEP 1100, a determination is made as to whether the protection guard enablement indicator is enabled, INQUIRY 1102. If it is enabled, then the guard word value is obtained from the guard word register or other selected location, STEP 1104, and stored in the memory location, specified by the address of the STPGC, STEP 1106. The instruction then completes, STEP 1108. Otherwise, if the protection guard enablement indicator is not enabled, then the instruction completes without obtaining the guard word value or storing it in the stack, STEP 1108.

Likewise, further details relating to the POPCHECK Conditional instruction are described with reference to FIG. 12. In one embodiment, based on initiating execution of the POPCHECK Conditional instruction, STEP 1200, a determination is made as to whether the protection guard enablement indicator is enabled, INQUIRY 1202. If it is enabled, then the guard word is loaded from the top of the stack, STEP 1204, and the stack pointer is moved above the guard word, such that it appears the guard word has been removed, although it remains in memory, STEP 1205. The guard word value is obtained from the guard word register or other selected location, STEP 1206, and the guard words from the top of the stack and the guard word register are compared. If there is a mismatch, INQUIRY 1208, then an indication is provided of corruption, STEP 1210. Otherwise, the instruction completes, STEP 1212.

Returning to INQUIRY 1202, if the protection guard enablement indicator is disabled, then the stack pointer is moved, as above, STEP 1211, and processing continues to STEP 1212. The instruction completes without loading or obtaining the guard word or performing the compare.

One example of code using the conditional store and verify instructions is described below (in one example of a CISC instruction set architecture):

Subroutine call: Store Guard Word Cond -20 [ESP] push [var]      ; Push last parameter first push 216      ; Push the second parameter push eax      ; Push first parameter last call_myFunc      ; Call the function add esp, 12      ; Remove the 3 parms upon return Callee       .486       .Model Flat        .Code        PUBLIC_myFunc        _myFunc Proc        ;Subrouting Prolog        SUB ESP, 4      ; Skip Guard Word push ebp      ; Save the old base pointer move ebp, esp      ; Set the new base pointer value sub esp, 4      ; Make room for one 4-byte local variable push edi      ; Save the values of registers function       push esi      ; Will modify. This func uses EDI and ESI ; Subroutine Body       <attack occurs here>       ; Subroutine Epilog       pop esi      ; Recover register values pop edi       move sp, ebp      , Deallocate local variables pop ebp      ; Restore the caller's base pointer value POPCHECK COND      ; Conditionally Pop and check guard word Ret      ; Obtain and remove address of caller from      stack; return to caller

In another embodiment of the example code hereinabove, the POPCHECK COND and RET instructions are replaced by a single POPCHECKRET COND instruction, or a merged instruction sequence. In accordance with such an embodiment, the POPCHECKRET COND instruction unconditionally retrieves the return address from the stack, conditionally (based on the guard word facility being enabled) retrieves the guard word from the stack, unconditionally moves the stack pointer across the guard word, and the return address, conditionally (based on the guard word facility being enabled) compares the conditionally loaded guard word with the reference guard word and based on determining a mismatch between the conditionally retrieved guard word and reference guard word, performs a corruption indication, and performs a return to the previously returned address unless a corruption notification has been performed (i.e., either unconditionally based on the guard word facility being disabled, or conditionally, based on the guard word facility being enabled, when no corruption has been detected).

Described above is one example of interlinking modules with possibly differing protection capabilities. In another example, instead of using the protection guard enablement indicator, a per-routine indication, implemented, for instance, as an enable vector of indicators, is used. In one example, as shown in FIG. 13, an enable vector 1300 (also referred to as an enable vector stack) may be a single bit shift register initialized to zero 1302. When a routine stores a guard word on the stack, it sets an indicator (e.g., to one) at the top of the enable vector stack 1304 to indicate that the routine has provided a protection guard word in its stack. When a routine is called, a new indicator is provided at the top of the stack. This may be achieved by shifting the shift register by one bit, indicating the presence of a new routine. When a routine returns, the shift register is shifted in the opposite direction.

Thus, in the examples above with the subroutine call and callee, based on the subroutine call (i.e., caller) storing a guard word on the stack, the subroutine caller sets an indicator 1306 in the vector (which would be at the top of the vector stack at the time of setting the indicator). Similarly, if the callee is to store a guard word on its stack, it also sets an indicator 1308.

Since the stack is of a defined size, if necessary, any shifted out indicators may be stored in backup storage. If no backup storage is used, then those routines for which indicators may have been shifted out may be executed without guard word protection by shifting in “0” corresponding to an indication that no indicator should be checked, in accordance with at least one embodiment.

In yet a further embodiment, if it is known that all of the routines have stack guard protection (e.g., by performing the techniques described herein), then the facility is configured to load ‘1’, or a single bit indicator is used causing guard word protection to occur regardless of the stack indicators.

In the enable vector indicators example, the Store Guard Word Conditional and POPCHECK Conditional instructions may be used, but the logic is a bit different. In this example, instead of the condition being based on the guard word protection enablement indicator, the condition is based on a value of a stack indicator retrieved from the enable vector.

For instance, in this example, the Store Guard Word Conditional instruction stores the guard word in the stack, and then sets the stack indicator in the enable vector (e) to e.g., one (indicator(eTOS) is set to true, where eTOS is top of stack of enable vector)). One embodiment of logic associated with this example of the Store Guard Word Conditional instruction, referred to as STPGC-2, is described with reference to FIG. 14.

Referring to FIG. 14, in one embodiment, based on executing the STPGC-2 instruction, the guard word value is obtained from the guard word register or other selected location, STEP 1400. That obtained value is then stored at the provided address of the instruction, STEP 1402. Then, in this embodiment, a stack indicator in the enable vector is set (e.g., indicator at eTOS is set to one), STEP 1404.

Further, in one example, the POPCHECK Conditional instruction verifies the guard word if the selected indicator indicates guard word protection (verify if indicator (eTOS+1), i.e., the indicator corresponding to the caller of the present routine, and reflecting whether the caller provided a stack guard word, is true). One embodiment of logic associated with this example of the POPCHECK Conditional instruction, referred to as POPCHECKC-2, is described with reference to FIG. 15.

Referring to FIG. 15, in one embodiment, execution of the instruction is initiated, STEP 1500, and a determination is made as to whether the indicator at the position of the enable vector (eTOS+1) is equal to one, INQUIRY 1502. If it is, the guard word value is loaded from the top of the stack, STEP 1504, and the stack pointer is moved, as described above, STEP 1505. The guard word value is obtained from the guard word register or other selected location, STEP 1506, and the guard word value from the stack is compared with the guard word value from the guard word register or other selected location. If there is not a match, INQUIRY 1508, then corruption is indicated, STEP 1510. Otherwise, if there is a match, then the instruction is completed, STEP 1512.

Returning to INQUIRY 1502, if the indicator in the enable vector is not set, then the stack pointer is moved, STEP 1511, and processing continues to STEP 1512.

In additional to the above, the POPCHECKRET may also be conditional.

In at least one embodiment, when a callee does not perform a POPCHECK instruction, the caller's indicator (eTOS+1) is reset to indicate that a guard word is not provided by the caller, e.g., during execution of the return from subroutine instruction. This reflects that the present routine appears not enabled for the protective guard word facility, resulting in the overwriting of the guard word by the present callee, thereby likely not having skipped the stack guard word to prevent its corruption and future use by other callees of the caller of the present routine.

The above allows the interlinking of modules or routines with or without differing protection capabilities. In one embodiment, the indicator is on a per-routine basis. A push down stack (e.g., enable vector) is provided that tracks for each routine level whether its stack has been protected by a guardword. A call subroutine allocates a new entry on the stack, and initializes the entry to unprotected. A Store Guard Word instruction or other store protection word instruction is executed by the call subroutine that concurrently updates the push down stack to indicate that stack protection has been enabled for the routine's callees. When the stack has been protected by a caller, the callee executes a POPCHECK instruction or other verify protection word instruction to verify the guard word. Otherwise, verification is suppressed, in one example. Other embodiments are possible.

As described herein, the detection of corruption of stacks is facilitated. One embodiment of logic relating to detecting corruption of stacks is described with reference to FIGS. 16A-16B.

Referring to FIG. 16A, in one embodiment, a called routine executing on a processor of the computing environment checks a guard word provided by a calling routine, STEP 1600. The calling routine called the called routine, and the guard word is stored in a stack of the calling routine, and protects a return address stored directly into the stack by a hardware instruction, STEP 1602.

Based on the checking, a determination is made as to whether the guard word has an expected value, STEP 1604. Based on determining the guard word has an unexpected value, providing an indication of corruption of the stack, STEP 1606.

In one example, at least the checking and the determining are performed via an instruction issued by the called routine, STEP 1608. The instruction is executed, STEP 1610, and the executing may include: obtaining the guard word from the stack, STEP 1612; moving a stack pointer of the stack such that the guard word no longer appears on the stack, STEP 1614; and performing one or more of the determining, the checking and the providing an indication, STEP 1616.

The executing further includes determining whether the calling routine supports use of the guard word to protect the return address, STEP 1618. Based on determining the calling routine supports use of the guard word, performing the obtaining, the moving and the performing, STEP 1620.

The guard word is provided, in one example, using a store guard word instruction that specifies an address for the guard word, STEP 1622.

Referring to FIG. 16B, an indicator may be set to indicate that the calling routine supports use of the guard word to protect the return address, STEP 1630.

In a further aspect, a determination is made as to whether the calling routine and the called routine support use of the guard word to protect the return address, STEP 1632. Based on determining that the calling routine and the called routine support use of the guard word to protect the return address, performing one or more of the checking, the determining and the providing an indication, STEP 1634. Based on determining that at least one routine of the calling routine and the called routine does not support use of the guard word to protect the return address, terminating processing prior to the checking, STEP 1636.

In one embodiment, the determining whether the calling routine and the called routine support use of the guard word to protect the return address includes checking at least one indicator, STEP 1638. The at least one indicator may be stored in a vector of indicators, STEP 1640.

Although examples are described herein, other embodiments are possible. For instance, in one embodiment, guard words may not be allocated in leaf functions, which further reduces overhead of performing writes; and a guard word may not be checked if a return address was not stored in the stack, thereby reducing the overhead of checking.

In at least one embodiment, the guard word includes a “\0” character (or other appropriate terminator), further ensuring that most overflows would terminate due to a termination character. This avoids overflow attacks with most vulnerable (string) functions if a guard character is reconstructed, because overwriting the guard character “correctly” would implicitly terminate an overwrite attack at that point.

In one embodiment, the guard word is randomized during every execution, and initialized by the operating system when a new program is executed.

In a further aspect, stack protection may be disabled by a programmer, operator, supervisor user and/or other agent. In yet another embodiment, the protection may be disabled based on system load or based on other selected criteria.

Described herein is a low-overhead mechanism for protecting return addresses stored directly into a stack by a hardware instruction, such as a jump subroutine instruction used for instance in CISC architectures.

In one example, with the hardware-managed stack and subroutine call, the subroutine instruction deposits the return address to the top of stack, the caller deposits the guard word below the stack and the called function is to “skip” the guard word when allocating its own frame. Processing is provided to handle this situation.

In one aspect, the checking of the guard word comes before the retrieval and use of the return address, because the retrieval of the return address is directly linked with the transfer thereto—at which point it is too late to do the check. Hence, POPCHECKRET, i.e., an instruction retrieving the return word, then checking the guard word, then returning to the caller in a single instruction, enables security not previously provided. In another embodiment, a microarchitectural embodiment fuses a sequence of instructions to check the guard word and perform a return. POPCHECKRET (either as a single instruction or a fused sequence) can safely and without any period of an unprotected return address execute a check and return.

One or more aspects may relate to cloud computing.

It is understood in advance that although this disclosure includes a detailed description on cloud computing, implementation of the teachings recited herein are not limited to a cloud computing environment. Rather, embodiments of the present invention are capable of being implemented in conjunction with any other type of computing environment now known or later developed.

Cloud computing is a model of service delivery for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g. networks, network bandwidth, servers, processing, memory, storage, applications, virtual machines, and services) that can be rapidly provisioned and released with minimal management effort or interaction with a provider of the service. This cloud model may include at least five characteristics, at least three service models, and at least four deployment models.

Characteristics are as follows:

On-demand self-service: a cloud consumer can unilaterally provision computing capabilities, such as server time and network storage, as needed automatically without requiring human interaction with the service's provider.

Broad network access: capabilities are available over a network and accessed through standard mechanisms that promote use by heterogeneous thin or thick client platforms (e.g., mobile phones, laptops, and PDAs).

Resource pooling: the provider's computing resources are pooled to serve multiple consumers using a multi-tenant model, with different physical and virtual resources dynamically assigned and reassigned according to demand. There is a sense of location independence in that the consumer generally has no control or knowledge over the exact location of the provided resources but may be able to specify location at a higher level of abstraction (e.g., country, state, or datacenter).

Rapid elasticity: capabilities can be rapidly and elastically provisioned, in some cases automatically, to quickly scale out and rapidly released to quickly scale in. To the consumer, the capabilities available for provisioning often appear to be unlimited and can be purchased in any quantity at any time.

Measured service: cloud systems automatically control and optimize resource use by leveraging a metering capability at some level of abstraction appropriate to the type of service (e.g., storage, processing, bandwidth, and active user accounts). Resource usage can be monitored, controlled, and reported providing transparency for both the provider and consumer of the utilized service.

Service Models are as follows:

Software as a Service (SaaS): the capability provided to the consumer is to use the provider's applications running on a cloud infrastructure. The applications are accessible from various client devices through a thin client interface such as a web browser (e.g., web-based email). The consumer does not manage or control the underlying cloud infrastructure including network, servers, operating systems, storage, or even individual application capabilities, with the possible exception of limited user-specific application configuration settings.

Platform as a Service (PaaS): the capability provided to the consumer is to deploy onto the cloud infrastructure consumer-created or acquired applications created using programming languages and tools supported by the provider. The consumer does not manage or control the underlying cloud infrastructure including networks, servers, operating systems, or storage, but has control over the deployed applications and possibly application hosting environment configurations.

Infrastructure as a Service (IaaS): the capability provided to the consumer is to provision processing, storage, networks, and other fundamental computing resources where the consumer is able to deploy and run arbitrary software, which can include operating systems and applications. The consumer does not manage or control the underlying cloud infrastructure but has control over operating systems, storage, deployed applications, and possibly limited control of select networking components (e.g., host firewalls).

Deployment Models are as follows:

Private cloud: the cloud infrastructure is operated solely for an organization. It may be managed by the organization or a third party and may exist on-premises or off-premises.

Community cloud: the cloud infrastructure is shared by several organizations and supports a specific community that has shared concerns (e.g., mission, security requirements, policy, and compliance considerations). It may be managed by the organizations or a third party and may exist on-premises or off-premises.

Public cloud: the cloud infrastructure is made available to the general public or a large industry group and is owned by an organization selling cloud services.

Hybrid cloud: the cloud infrastructure is a composition of two or more clouds (private, community, or public) that remain unique entities but are bound together by standardized or proprietary technology that enables data and application portability (e.g., cloud bursting for loadbalancing between clouds).

A cloud computing environment is service oriented with a focus on statelessness, low coupling, modularity, and semantic interoperability. At the heart of cloud computing is an infrastructure comprising a network of interconnected nodes.

A cloud computing node may include a computer system/server, such as the one depicted in FIG. 1. Computer system/server 102 of FIG. 1 may be practiced in distributed cloud computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed cloud computing environment, program modules may be located in both local and remote computer system storage media including memory storage devices. Computer system/server 102 is capable of being implemented and/or performing any of the functionality set forth hereinabove.

Referring now to FIG. 17, illustrative cloud computing environment 50 is depicted. As shown, cloud computing environment 50 comprises one or more cloud computing nodes 10 with which local computing devices used by cloud consumers, such as, for example, personal digital assistant (PDA) or cellular telephone 54A, desktop computer 54B, laptop computer 54C, and/or automobile computer system 54N may communicate. Nodes 10 may communicate with one another. They may be grouped (not shown) physically or virtually, in one or more networks, such as Private, Community, Public, or Hybrid clouds as described hereinabove, or a combination thereof. This allows cloud computing environment 50 to offer infrastructure, platforms and/or software as services for which a cloud consumer does not need to maintain resources on a local computing device. It is understood that the types of computing devices 54A-N shown in FIG. 6 are intended to be illustrative only and that computing nodes 10 and cloud computing environment 50 can communicate with any type of computerized device over any type of network and/or network addressable connection (e.g., using a web browser).

Referring now to FIG. 18, a set of functional abstraction layers provided by cloud computing environment 50 (FIG. 17) is shown. It should be understood in advance that the components, layers, and functions shown in FIG. 18 are intended to be illustrative only and embodiments of the invention are not limited thereto. As depicted, the following layers and corresponding functions are provided:

Hardware and software layer 60 includes hardware and software components. Examples of hardware components include mainframes 61; RISC (Reduced Instruction Set Computer) architecture based servers 62; servers 63; blade servers 64; storage devices 65; and networks and networking components 66. In some embodiments, software components include network application server software 67 and database software 68.

Virtualization layer 70 provides an abstraction layer from which the following examples of virtual entities may be provided: virtual servers 71; virtual storage 72; virtual networks 73, including virtual private networks; virtual applications and operating systems 74; and virtual clients 75.

In one example, management layer 80 may provide the functions described below. Resource provisioning 81 provides dynamic procurement of computing resources and other resources that are utilized to perform tasks within the cloud computing environment. Metering and Pricing 82 provide cost tracking as resources are utilized within the cloud computing environment, and billing or invoicing for consumption of these resources. In one example, these resources may comprise application software licenses. Security provides identity verification for cloud consumers and tasks, as well as protection for data and other resources. User portal 83 provides access to the cloud computing environment for consumers and system administrators. Service level management 84 provides cloud computing resource allocation and management such that required service levels are met. Service Level Agreement (SLA) planning and fulfillment 85 provide pre-arrangement for, and procurement of, cloud computing resources for which a future requirement is anticipated in accordance with an SLA.

Workloads layer 90 provides examples of functionality for which the cloud computing environment may be utilized. Examples of workloads and functions which may be provided from this layer include: mapping and navigation 91; software development and lifecycle management 92; virtual classroom education delivery 93; data analytics processing 94; transaction processing 95; and stack protection processing 96.

Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.

These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks.

The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

In addition to the above, one or more aspects may be provided, offered, deployed, managed, serviced, etc. by a service provider who offers management of customer environments. For instance, the service provider can create, maintain, support, etc. computer code and/or a computer infrastructure that performs one or more aspects for one or more customers. In return, the service provider may receive payment from the customer under a subscription and/or fee agreement, as examples. Additionally or alternatively, the service provider may receive payment from the sale of advertising content to one or more third parties.

In one aspect, an application may be deployed for performing one or more embodiments. As one example, the deploying of an application comprises providing computer infrastructure operable to perform one or more embodiments.

As a further aspect, a computing infrastructure may be deployed comprising integrating computer readable code into a computing system, in which the code in combination with the computing system is capable of performing one or more embodiments.

As yet a further aspect, a process for integrating computing infrastructure comprising integrating computer readable code into a computer system may be provided. The computer system comprises a computer readable medium, in which the computer medium comprises one or more embodiments. The code in combination with the computer system is capable of performing one or more embodiments.

Although various embodiments are described above, these are only examples. For example, computing environments of other architectures can be used to incorporate and use one or more embodiments. Further, different types of guard words may be used. Many variations are possible.

Further, other types of computing environments can benefit and be used. As an example, a data processing system suitable for storing and/or executing program code is usable that includes at least two processors coupled directly or indirectly to memory elements through a system bus. The memory elements include, for instance, local memory employed during actual execution of the program code, bulk storage, and cache memory which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution.

Input/Output or I/O devices (including, but not limited to, keyboards, displays, pointing devices, DASD, tape, CDs, DVDs, thumb drives and other memory media, etc.) can be coupled to the system either directly or through intervening I/O controllers. Network adapters may also be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modems, and Ethernet cards are just a few of the available types of network adapters.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of one or more embodiments has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain various aspects and the practical application, and to enable others of ordinary skill in the art to understand various embodiments with various modifications as are suited to the particular use contemplated. 

What is claimed is:
 1. A computer program product for detecting corruption of stacks of a computing environment, said computer program product comprising: a computer readable storage medium readable by a processing circuit and storing instructions for performing a method comprising: checking, by a called routine executing on a processor of the computing environment, a guard word provided by a calling routine, the calling routine having called the called routine, and the guard word being stored in a stack of the calling routine and protecting a return address stored directly into the stack by a hardware instruction; determining, based on the checking, whether the guard word has an expected value; and based on determining the guard word has an unexpected value, providing an indication of corruption of the stack.
 2. The computer program product of claim 1, wherein at least the checking and the determining are performed via an instruction issued by the called routine.
 3. The computer program product of claim 2, wherein the method further includes executing the instruction, the executing including: obtaining the guard word from the stack; moving a stack pointer of the stack such that the guard word no longer appears on the stack; and performing one or more of the determining, the checking and the providing an indication.
 4. The computer program product of claim 3, wherein the executing further comprises: determining whether the calling routine supports use of the guard word to protect the return address; and based on determining the calling routine supports use of the guard word, performing the obtaining, the moving and the performing.
 5. The computer program product of claim 1, wherein the guard word is provided using a store guard word instruction that specifies an address for the guard word.
 6. The computer program product of claim 1, wherein the method further comprises: providing the guard word using a store guard word instruction; and setting an indicator to indicate that the calling routine supports use of the guard word to protect the return address.
 7. The computer program product of claim 1, wherein the method further comprises: determining whether the calling routine and the called routine support use of the guard word to protect the return address; and based on determining that the calling routine and the called routine support use of the guard word to protect the return address, performing one or more of the checking, the determining and the providing an indication.
 8. The computer program of claim 7, wherein the method further comprises based on determining that at least one routine of the calling routine and the called routine does not support use of the guard word to protect the return address, terminating processing prior to the checking.
 9. The computer program product of claim 7, wherein the determining whether the calling routine and the called routine support use of the guard word to protect the return address comprises checking at least one indicator.
 10. The computer program product of claim 9, wherein the at least one indicator is stored in a vector of indicators.
 11. A computer system for detecting corruption of stacks of a computing environment, said computer system comprising: a memory; and a processor in communication with the memory, wherein the computer system is configured to perform a method, said method comprising: checking, by a called routine executing on a processor of the computing environment, a guard word provided by a calling routine, the calling routine having called the called routine, and the guard word being stored in a stack of the calling routine and protecting a return address stored directly into the stack by a hardware instruction; determining, based on the checking, whether the guard word has an expected value; and based on determining the guard word has an unexpected value, providing an indication of corruption of the stack.
 12. The computer system of claim 11, wherein at least the checking and the determining are performed via an instruction issued by the called routine, and wherein the method further includes executing the instruction, the executing including: obtaining the guard word from the stack; moving a stack pointer of the stack such that the guard word no longer appears on the stack; and performing one or more of the determining, the checking and the providing an indication.
 13. The computer system of claim 12, wherein the executing further comprises: determining whether the calling routine supports use of the guard word to protect the return address; and based on determining the calling routine supports use of the guard word, performing the obtaining, the moving and the performing.
 14. The computer system of claim 11, wherein the guard word is provided using a store guard word instruction that specifies an address for the guard word.
 15. The computer system of claim 11, wherein the method further comprises: providing the guard word using a store guard word instruction; and setting an indicator to indicate that the calling routine supports use of the guard word to protect the return address.
 16. A computer-implemented method of detecting corruption of stacks of a computing environment, said computer-implemented method comprising: checking, by a called routine executing on a processor of the computing environment, a guard word provided by a calling routine, the calling routine having called the called routine, and the guard word being stored in a stack of the calling routine and protecting a return address stored directly into the stack by a hardware instruction; determining, based on the checking, whether the guard word has an expected value; and based on determining the guard word has an unexpected value, providing an indication of corruption of the stack.
 17. The computer-implemented method of claim 16, wherein at least the checking and the determining are performed via an instruction issued by the called routine, and wherein the method further includes executing the instruction, the executing including: obtaining the guard word from the stack; moving a stack pointer of the stack such that the guard word no longer appears on the stack; and performing one or more of the determining, the checking and the providing an indication.
 18. The computer-implemented method of claim 17, wherein the executing further comprises: determining whether the calling routine supports use of the guard word to protect the return address; and based on determining the calling routine supports use of the guard word, performing the obtaining, the moving and the performing.
 19. The computer-implemented method of claim 16, wherein the guard word is provided using a store guard word instruction that specifies an address for the guard word.
 20. The computer-implemented method of claim 16, further comprising: providing the guard word using a store guard word instruction; and setting an indicator to indicate that the calling routine supports use of the guard word to protect the return address. 